The invention is directed to a photosetting apparatus, particularly a laser exposer, having a cylindrical bed wherein a sheet-shaped photo material is transported into the cylindrical bed and placed against and inside thereof. An exposure optics having a rotatable portion is displaceable along a direction of a longitudinal axis of the cylindrical bed.
In such a photosetting apparatus having a cylindrical bed, which can also be referred to as a circular cylindrical segment, a part of the exposure optics, particularly a rotating mirror, is rotatable around the longitudinal axis of the cylindrical bed and is displaceable in the direction thereof in order to expose photomaterial along scan lines. This photomaterial is held inside at the cylindrical bed and has its light-sensitive layer directed toward the longitudinal axis of the cylindrical bed. Since the same path section from the rotating mirror up to the light-sensitive layer is always bridged for this purpose, and since the ray beam always impinges the light-sensitive material at the same angle, advantages derive, particularly due to a simple imaging optics and a uniform, sharp exposure of constant exposure intensity for the entire format to be exposed.
In such a photosetting apparatus having a cylindrical bed, however, the sheet-shaped photomaterial must be conveyed from an approximately planar position in which it is normally most simply conveyed into the curved cylindrical bed and must be held pressing against the inside of the cylindrical bed before the exposure event can occur. For this purpose the photomaterial in a known photosetting apparatus (German Patent 36 04 360) of this type is conveyed into the cylindrical bed through an open jacket section in the direction of the inside circumference thereof while being guided, and is pulled from the cylindrical bed after the exposure event in an analogous way. The conveying event in the cylindrical bed thus occurs in a circumferential direction thereof. For this purpose, two guide rings each comprising a front stop and introduced into the cylindrical bed or circular cylindrical segment with axial spacing are provided in detail as guide elements that engage at lateral edges of the photomaterial. The outside diameters of these guide rings correspond to the inside diameter of the cylindrical bed or, respectively, of the circular cylindrical segment. Axially extending guide members are provided before the start and following the end of the exposure region. These guide members guide the photomaterial along its breadth and convey it into the curvature of the inside of the circular cylindrical segment in the fashion of a restricted guidance. What is thereby disadvantageous is that plates--such as photomaterial that is to be directly exposed--can only be introduced with difficulty because of the stiffness of the printing plates, since they must be conveyed in the curved shape within the circular cylindrical segment after they were curved upon introduction. Scratches can easily occur in this curving process and in the following conveying process. These can be entirely avoided only with auxiliary devices that increase the expense. Furthermore, photomaterials of arbitrary length cannot be processed without further ado; on the contrary, conveying these through the circular cylindrical segment would likewise assume comparatively complicated auxiliary devices.